That sinking feeling: My science inquiry project about quicksand

My students are currently working in the Land & Water science kit.  They have been learning about groundwater, absorption, runoff, stream patterns, and rain.  They have big tubs of different types of soil components and they add water.

Really we have just learning about the world around us by making, and playing with, mud each day (how is this not the best profession ever?).

This adding of water to clay and sand got me to thinking about quicksand.  It seemed like a fun thing to play with and it tied in nicely with the whole land and water theme.  I have always wondered if the weight and size of a person made a difference in how fast they sunk in quicksand (there's a sleight chance I may have watched too many jungle explorer movies, or played a few too many games of Pitfall as a kid).  Does the small, wiry scientist sink just as fast as the hulking, neck-less poacher?
 
In order to set up an experiment to find this out I would need some quicksand.  Apparently, in the scientific world, we do our experiments about quicksand using Gooblex.  It's a corn-starch and water mix, also known as a "non-Newtonian fluid", that behaves just like quicksand; quick movements meet fierce resistance, while slow movements are allowed.  I decided to make some in order to see if it would both be doable by my students, and serve our quicksand needs.

  I mixed 16oz of cornstarch with 2 cups of water (green food coloring optional).  The whole thing only took about ten minutes, so it met my time criteria, and it seemingly will work for my quicksand tests.  Even if you don't want to do the science, it's pretty weird stuff and fun to make.

Now that I knew I had a viable quicksand, I could form a question for the kids to explore.  I'm still working of this part, so bear with me, but here's my idea so far:

Question:
Does the size, weight, and shape of an object affect how fast it will sink in quicksand?

My plan is to have the kids make their "quicksand" in a 500ml container (the ones we are using are approx. 5" across and 8" tall).  They can then use masking tape to mark a point 3" below the top line of their "quicksand".  I am thinking that if we use the same size and shape objects (our fixed variable) of different weights (changed variable), we can chart the data on a table like this:

From there we can alter the fixed and changed variables to see the effects of size and shape. 

I may need to shorten this to simply being about weight.  Making the "quicksand" and conducting this first phase of the experiment would be a full days lesson in itself.  The "non-Newtonian" fluid doesn't last overnight, I checked.  The water and corn starch separate from one another and the water evaporates, leaving a hard crusty substance behind.

Well, there it is so far.  I will keep you updated on changes and progress.  Let me know what you think, or if you have any ideas.